Distributed scheduling in a virtual machine environment

ABSTRACT

A first scheduler stores into a memory of a first virtual machine, a first block of jobs to be executed by the first virtual machine, the first block of jobs included in a table stored in a database associated with a server computer system. A second scheduler stores into a memory of a second virtual machine, a second block of jobs to be executed by the second virtual machine. The second block of jobs being included in the table and having a second block size equal to the first block size and including jobs not in the first block. From the first virtual machine memory, the first scheduler schedules one or more jobs in the first block for execution by the first virtual machine. From the second virtual machine memory, the second scheduler schedules one or more jobs in the second block for execution by the second virtual machine.

PRIORITY CLAIM AND RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/601,199 filed May 22, 2017, now U.S. Pat. No. 10,318,349, the entirecontents of which are incorporated herein by reference as if set forthin full herein.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

TECHNICAL FIELD

The present disclosure relates generally to data processing and morespecifically relates to distributed scheduling.

BACKGROUND

The subject matter discussed in the background section should not beassumed to be prior art merely as a result of its mention in thebackground section. Similarly, a problem mentioned in the backgroundsection or associated with the subject matter of the background sectionshould not be assumed to have been previously recognized in the priorart. The subject matter in the background section merely representsdifferent approaches, which in and of themselves may also be inventions.

In general, there may be multiple processing systems in a distributedenvironment, with each processing system configured to perform its shareof the workload. For example, the workload may include multiple jobs.The jobs may be stored in a database. Each processing system may beassociated with a scheduler. Each scheduler may be configured to acquirea job from the database based on a trigger. Typically, when a triggeroccurs, a scheduler acquires a job associated with the trigger and firesthe trigger. This causes the job to be executed. A lock may be used toenable the scheduler to update the trigger. This approach may work finewhen the number of triggers is low. However, when the number of triggersincreases, the above approach may cause many triggers to miss theirscheduled firing time resulting in missing execution of jobs, amongother problems.

BRIEF SUMMARY

For some embodiments, methods for distributed scheduling of jobs mayinclude storing by a first scheduler into a memory of a first virtualmachine running on a server computer system, a first block of jobs to beexecuted by the first virtual machine, the first block of jobs beingincluded in a job table stored in a database and having a first blocksize, the database associated with the server computer system; storingby a second scheduler into a memory of a second virtual machine runningon the server computer system, a second block of jobs to be executed bythe by the second virtual machine, the second block of jobs beingincluded in the job table and having a second block size, the secondblock size being equal to the first block size and including jobs thatare not in included in the first block of jobs; scheduling by the firstscheduler from the memory of the first virtual machine, one or more jobsin the first block of jobs for execution by the first virtual machine;and scheduling by the second scheduler from the memory of the secondvirtual machine, one or more jobs in the second block of jobs forexecution by the second virtual machine. Other aspects and advantages ofthe present invention can be seen on review of the drawings, thedetailed description and the claims, which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The included drawings are for illustrative purposes and serve only toprovide examples of possible structures and process steps for thedisclosed techniques. These drawings in no way limit any changes in formand detail that may be made to embodiments by one skilled in the artwithout departing from the spirit and scope of the disclosure.

FIG. 1 shows a diagram of an example computing system that may be usedwith some embodiments.

FIG. 2 shows a diagram of an example network environment that may beused with some embodiments.

FIG. 3 shows an example diagram of a cluster of machines that may beused, in accordance with some embodiments.

FIG. 4 shows an example distributed scheduling lock table, in accordancewith some embodiments.

FIG. 5 shows an example of the schedulers using the distributedscheduling lock table to schedule jobs, in accordance with someembodiments.

FIG. 6 shows a flowchart of an example process that may be performed bya scheduler to read jobs from a job table, in accordance with someembodiments.

FIG. 7A shows a flowchart of an example of a process that may beperformed by a scheduler to determine whether there are jobs to bescheduled, in accordance with some embodiments.

FIG. 7B shows a flow chart example of a process that may be performedbased on a refresh cycle, in accordance with some embodiments.

FIG. 8A shows a system diagram illustrating architectural components ofan applicable environment, in accordance with some embodiments.

FIG. 8B shows a system diagram further illustrating architecturalcomponents of an applicable environment, in accordance with someembodiments.

FIG. 9 shows a system diagram illustrating the architecture of amulti-tenant database environment, in accordance with some embodiments.

FIG. 10 shows a system diagram further illustrating the architecture ofa multi-tenant database environment, in accordance with someembodiments.

DETAILED DESCRIPTION

Systems and methods for distributed scheduling of jobs are disclosed.Jobs in a job table may be read into memories of virtual machines byschedulers associated with those virtual machines. The virtual machinesmay be configured to support load balancing and failovers. The jobs maybe read as a block of jobs based on a block size. A scheduler may thenschedule the jobs in the block of jobs from the memory of a virtualmachine. An index may be used to determine a first job of a block. Ascheduling refresh may occur based on a refresh cycle to reset theblocks of jobs associated with each of the virtual machines.

The systems and methods will be described with reference to exampleembodiments. These examples are being provided solely to add context andaid in the understanding of the present disclosure. It will thus beapparent to one skilled in the art that the techniques described hereinmay be practiced without some or all of these specific details. In otherinstances, well known process steps have not been described in detail inorder to avoid unnecessarily obscuring the present disclosure. Otherapplications are possible, such that the following examples should notbe taken as definitive or limiting either in scope or setting.

In the following detailed description, references are made to theaccompanying drawings, which form a part of the description and in whichare shown, by way of illustration, specific embodiments. Although theseembodiments are described in sufficient detail to enable one skilled inthe art to practice the disclosure, it is understood that these examplesare not limiting, such that other embodiments may be used and changesmay be made without departing from the spirit and scope of thedisclosure.

As used herein, the term “multi-tenant database system” refers to thosesystems in which various elements of hardware and software of thedatabase system may be shared by one or more customers. For example, agiven application server may simultaneously process requests for a greatnumber of customers, and a given database table may store rows for apotentially much greater number of customers.

The described subject matter may be implemented in the context of anycomputer-implemented system, such as a software-based system, a databasesystem, a multi-tenant environment, or the like. Moreover, the describedsubject matter may be implemented in connection with two or moreseparate and distinct computer-implemented systems that cooperate andcommunicate with one another. One or more embodiments may be implementedin numerous ways, including as a process, an apparatus, a system, adevice, a method, a computer readable medium such as a computer readablestorage medium containing computer readable instructions or computerprogram code, or as a computer program product comprising a computerusable medium having a computer readable program code embodied therein.

The disclosed embodiments may include systems and methods fordistributed scheduling of jobs. The method may include storing by afirst scheduler into a memory of a first virtual machine running on aserver computer system, a first block of jobs to be executed by thefirst virtual machine, the first block of jobs being included in a jobtable stored in a database and having a first block size, the databaseassociated with the server computer system; storing by a secondscheduler into a memory of a second virtual machine running on theserver computer system, a second block of jobs to be executed by the bythe second virtual machine, the second block of jobs being included inthe job table and having a second block size, the second block sizebeing equal to the first block size and including jobs that are not inincluded in the first block of jobs; scheduling by the first schedulerfrom the memory of the first virtual machine, one or more jobs in thefirst block of jobs for execution by the first virtual machine; andscheduling by the second scheduler from the memory of the second virtualmachine, one or more jobs in the second block of jobs for execution bythe second virtual machine.

The disclosed embodiments may include an apparatus for performingdistributed scheduling of jobs and include a processor, and one or morestored sequences of instructions which, when executed by the processor,cause the processor to store by a first scheduler into a memory of afirst virtual machine running on a server computer system, a first blockof jobs to be executed by the first virtual machine, the first block ofjobs being included in a job table stored in a database and having afirst block size, the database associated with the server computersystem; store by a second scheduler into a memory of a second virtualmachine running on the server computer system, a second block of jobs tobe executed by the second virtual machine, the second block of jobsbeing included in the job table and having a second block size, thesecond block size being equal to the first block size and including jobsthat are not in included in the first block of jobs; schedule by thefirst scheduler from the memory of the first virtual machine, one ormore jobs in the first block of jobs for execution by the first virtualmachine; and schedule by the second scheduler from the memory of thesecond virtual machine, one or more jobs in the second block of jobs forexecution by the second virtual machine.

The disclosed embodiments may include a computer program productcomprising computer-readable program code to be executed by one or moreprocessors when retrieved from a non-transitory computer-readablemedium, the program code including instructions to store by a firstscheduler into a memory of a first virtual machine running on a servercomputer system, a first block of jobs to be executed by the firstvirtual machine, the first block of jobs being included in a job tablestored in a database and having a first block size, the databaseassociated with the server computer system; store by a second schedulerinto a memory of a second virtual machine running on the server computersystem, a second block of jobs to be executed by the second virtualmachine, the second block of jobs being included in the job table andhaving a second block size, the second block size being equal to thefirst block size and including jobs that are not in included in thefirst block of jobs; schedule by the first scheduler from the memory ofthe first virtual machine, one or more jobs in the first block of jobsfor execution by the first virtual machine; and schedule by the secondscheduler from the memory of the second virtual machine, one or morejobs in the second block of jobs for execution by the second virtualmachine.

While one or more implementations and techniques are described withreference to an embodiment in which jobs are scheduled from a memory ofa virtual machine is implemented in a system having an applicationserver providing a front end for an on-demand database service capableof supporting multiple tenants, the one or more implementations andtechniques are not limited to multi-tenant databases nor deployment onapplication servers. Embodiments may be practiced using other databasearchitectures, i.e., ORACLE®, DB2® by IBM and the like without departingfrom the scope of the embodiments claimed.

Any of the above embodiments may be used alone or together with oneanother in any combination. The one or more implementations encompassedwithin this specification may also include embodiments that are onlypartially mentioned or alluded to or are not mentioned or alluded to atall in this brief summary or in the abstract. Although variousembodiments may have been motivated by various deficiencies with theprior art, which may be discussed or alluded to in one or more places inthe specification, the embodiments do not necessarily address any ofthese deficiencies. In other words, different embodiments may addressdifferent deficiencies that may be discussed in the specification. Someembodiments may only partially address some deficiencies or just onedeficiency that may be discussed in the specification, and someembodiments may not address any of these deficiencies.

The described subject matter may be implemented in the context of anycomputer-implemented system, such as a software-based system, a databasesystem, a multi-tenant environment, or the like. Moreover, the describedsubject matter may be implemented in connection with two or moreseparate and distinct computer-implemented systems that cooperate andcommunicate with one another. One or more implementations may beimplemented in numerous ways, including as a process, an apparatus, asystem, a device, a method, a computer readable medium such as acomputer readable storage medium containing computer readableinstructions or computer program code, or as a computer program productcomprising a computer usable medium having a computer readable programcode embodied therein.

FIG. 1 is a diagram of an example computing system that may be used withsome embodiments of the present invention. The computing system 102 maybe used by a user to log into a server computing system and causeexecution of jobs using distributed scheduling services. For someembodiments, the server computing system may be associated with amulti-tenant database environment. For example, the multi-tenantdatabase environment may be associated with the services provided bySalesforce.com®.

The computing system 102 is only one example of a suitable computingsystem, such as a mobile computing system, and is not intended tosuggest any limitation as to the scope of use or functionality of thedesign. Neither should the computing system 102 be interpreted as havingany dependency or requirement relating to any one or combination ofcomponents illustrated. The design is operational with numerous othergeneral purpose or special purpose computing systems. Examples ofwell-known computing systems, environments, and/or configurations thatmay be suitable for use with the design include, but are not limited to,personal computers, server computers, hand-held or laptop devices,multiprocessor systems, microprocessor-based systems, set top boxes,programmable consumer electronics, mini-computers, mainframe computers,distributed computing environments that include any of the above systemsor devices, and the like. For example, the computing system 102 may beimplemented as a mobile computing system such as one that is configuredto run with an operating system (e.g., iOS) developed by Apple Inc. ofCupertino, Calif. or an operating system (e.g., Android) that isdeveloped by Google Inc. of Mountain View, Calif.

Some embodiments of the present invention may be described in thegeneral context of computing system executable instructions, such asprogram modules, being executed by a computer. Generally, programmodules include routines, programs, objects, components, datastructures, etc. that performs particular tasks or implement particularabstract data types. Those skilled in the art can implement thedescription and/or figures herein as computer-executable instructions,which can be embodied on any form of computing machine program productdiscussed below.

Some embodiments of the present invention may also be practiced indistributed computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network. Ina distributed computing environment, program modules may be located inboth local and remote computer storage media including memory storagedevices.

Referring to FIG. 1, the computing system 102 may include, but are notlimited to, a processing unit 120 having one or more processing cores, asystem memory 130, and a system bus 121 that couples various systemcomponents including the system memory 130 to the processing unit 120.The system bus 121 may be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. By way ofexample, and not limitation, such architectures include IndustryStandard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus,Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA)locale bus, and Peripheral Component Interconnect (PCI) bus also knownas Mezzanine bus.

The computing system 102 typically includes a variety of computerprogram product. Computer program product can be any available mediathat can be accessed by computing system 102 and includes both volatileand nonvolatile media, removable and non-removable media. By way ofexample, and not limitation, computer program product may storeinformation such as computer readable instructions, data structures,program modules or other data. Computer storage media include, but arenot limited to, RAM, ROM, EEPROM, flash memory or other memorytechnology, CD-ROM, digital versatile disks (DVD) or other optical diskstorage, magnetic cassettes, magnetic tape, magnetic disk storage orother magnetic storage devices, or any other medium which can be used tostore the desired information and which can be accessed by computingsystem 102. Communication media typically embodies computer readableinstructions, data structures, or program modules.

The system memory 130 may include computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 131and random access memory (RAM) 132. A basic input/output system (BIOS)133, containing the basic routines that help to transfer informationbetween elements within computing system 102, such as during start-up,is typically stored in ROM 131. RAM 132 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 120. By way of example, and notlimitation, FIG. 1 also illustrates operating system 134, applicationprograms 135, other program modules 136, and program data 137.

The computing system 102 may also include other removable/non-removablevolatile/nonvolatile computer storage media. By way of example only,FIG. 1 also illustrates a hard disk drive 141 that reads from or writesto non-removable, nonvolatile magnetic media, a magnetic disk drive 151that reads from or writes to a removable, nonvolatile magnetic disk 152,and an optical disk drive 155 that reads from or writes to a removable,nonvolatile optical disk 156 such as, for example, a CD ROM or otheroptical media. Other removable/non-removable, volatile/nonvolatilecomputer storage media that can be used in the exemplary operatingenvironment include, but are not limited to, USB drives and devices,magnetic tape cassettes, flash memory cards, digital versatile disks,digital video tape, solid state RAM, solid state ROM, and the like. Thehard disk drive 141 is typically connected to the system bus 121 througha non-removable memory interface such as interface 140, and magneticdisk drive 151 and optical disk drive 155 are typically connected to thesystem bus 121 by a removable memory interface, such as interface 150.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 1, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputing system 102. In FIG. 1, for example, hard disk drive 141 isillustrated as storing operating system 144, application programs 145,other program modules 146, and program data 147. Note that thesecomponents can either be the same as or different from operating system134, application programs 135, other program modules 136, and programdata 137. The operating system 144, the application programs 145, theother program modules 146, and the program data 147 are given differentnumeric identification here to illustrate that, at a minimum, they aredifferent copies.

A user may enter commands and information into the computing system 102through input devices such as a keyboard 162, a microphone 163, and apointing device 161, such as a mouse, trackball or touch pad or touchscreen. Other input devices (not shown) may include a joystick, gamepad, scanner, or the like. These and other input devices are oftenconnected to the processing unit 120 through a user input interface 160that is coupled with the system bus 121, but may be connected by otherinterface and bus structures, such as a parallel port, game port or auniversal serial bus (USB). A monitor 191 or other type of displaydevice is also connected to the system bus 121 via an interface, such asa video interface 190. In addition to the monitor, computers may alsoinclude other peripheral output devices such as speakers 197 and printer196, which may be connected through an output peripheral interface 190.

The computing system 102 may operate in a networked environment usinglogical connections to one or more remote computers, such as a remotecomputer 180. The remote computer 180 may be a personal computer, ahand-held device, a server, a router, a network PC, a peer device orother common network node, and typically includes many or all of theelements described above relative to the computing system 102. Thelogical connections depicted in

FIG. 1 includes a local area network (LAN) 171 and a wide area network(WAN) 173, but may also include other networks. Such networkingenvironments are commonplace in offices, enterprise-wide computernetworks, intranets and the Internet.

When used in a LAN networking environment, the computing system 102 maybe connected to the LAN 171 through a network interface or adapter 170.When used in a WAN networking environment, the computing system 102typically includes a modem 172 or other means for establishingcommunications over the WAN 173, such as the Internet. The modem 172,which may be internal or external, may be connected to the system bus121 via the user-input interface 160, or other appropriate mechanism. Ina networked environment, program modules depicted relative to thecomputing system 102, or portions thereof, may be stored in a remotememory storage device. By way of example, and not limitation, FIG. 1illustrates remote application programs 185 as residing on remotecomputer 180. It will be appreciated that the network connections shownare exemplary and other means of establishing a communications linkbetween the computers may be used.

It should be noted that some embodiments of the present invention may becarried out on a computing system such as that described with respect toFIG. 1. However, some embodiments of the present invention may becarried out on a server, a computer devoted to message handling,handheld devices, or on a distributed system in which different portionsof the present design may be carried out on different parts of thedistributed computing system.

Another device that may be coupled with the system bus 121 is a powersupply such as a battery or a Direct Current (DC) power supply) andAlternating Current (AC) adapter circuit. The DC power supply may be abattery, a fuel cell, or similar DC power source needs to be rechargedon a periodic basis. The communication module (or modem) 172 may employa Wireless Application Protocol (WAP) to establish a wirelesscommunication channel The communication module 172 may implement awireless networking standard such as Institute of Electrical andElectronics Engineers (IEEE) 802.11 standard, IEEE std. 802.11-1999,published by IEEE in 1999.

Examples of mobile computing systems may be a laptop computer, a tabletcomputer, a Netbook, a smart phone, a personal digital assistant, orother similar device with on board processing power and wirelesscommunications ability that is powered by a Direct Current (DC) powersource that supplies DC voltage to the mobile computing system and thatis solely within the mobile computing system and needs to be rechargedon a periodic basis, such as a fuel cell or a battery.

FIG. 2 shows a diagram of an example network environment that may beused with some embodiments of the present invention. Network environment200 includes computing systems 290 and 291. One or more of the computingsystems 290 and 291 may be a mobile computing system. The computingsystems 290 and 291 may be connected to the network 250 via a cellularconnection or via a Wi-Fi router (not shown). The network 250 may be theInternet. The computing systems 290 and 291 may be coupled with servercomputing system 255 via the network 250.

Each of the computing systems 290 and 291 may include a respectiveapplication module 208 and 214. A user may use the computing system 290and the application module 208 to connect to and communicate with theserver computing system 255 and log into application 257 (e.g., aSalesforce.com® application). The server computing system 255 may beassociated with a database 270. The database 270 may be configured tostore a job table that includes jobs to be executed using distributedscheduling.

FIG. 3 shows an example diagram of a cluster of machines that may beused, in accordance with some embodiments. Diagram 300 includes acluster 302 which may include machines 305, 306 and 307. Each of themachines 305, 306 and 307 may be configured as a virtual machine (or aninstance of a virtual machine). For example, the machine 305 may be aJava Virtual Machine (JVM) configured to provide a run time environmentfor a compiled Java program. The cluster 302 may be associated with ajob table 345 configured to store all jobs that are enabled forexecution. For example, a job may be a Java job and may include acompiled Java program or a set of compiled Java programs. A job may beassociated with a job definition. For example, the job definition mayindicate a job name, name of the Java program to execute, a start time,a stop time, a recurring frequency, etc. The job table 345 and thecluster 302 may be part of a scheduling service configured to schedulejobs in the job table 345 for execution.

The job table 345 may be stored in a database such as, for example, thedatabase 270 (shown in FIG. 2). The database 270 may be associated witha storage device such as, for example, a disk. For example, the jobtable 345 may be implemented as a table with a large number of rows.Each of the rows may correspond to a job and an index. For example, thefirst row may correspond to an index value of zero, the second row maycorrespond to an index value of one, and so on. The cluster 302 may beconfigured with load balancing and failover consideration. Loadbalancing indicates that the jobs in the job table 345 may bedistributed to the machines in the cluster 302 such that the workload isbalanced across all the machines. Failover indicates that if one of themachines in the cluster 302 fails, another machine in the cluster 302may take over the workload of the failed machine.

A scheduler (or scheduler instance) may be used to schedule a job forexecution. For some embodiments, each of the machines in the cluster 302may be configured to include a scheduler such as, for example, thescheduler 310, 311 or 312. The scheduling of a job may be associatedwith a trigger. For example, a job may be configured to execute hourlyat 15 minutes past the hour. The arrows connecting the job table 345 toeach of the machines 305, 306 and 307 are used to show that a job in thejob table 345 may be executed by any one of the machines 305, 306 and307. The job table 345 and the cluster 302 may be part of a schedulingservice. Upon start up, the scheduling service may immediately beginperforming operations to attempt to schedule the jobs in the job table345. The operations may include acquiring access to a distributedscheduling lock table 350 (shown in FIG. 4) and reading jobs from thejob table 345 into a memory of a machine.

FIG. 4 shows an example distributed scheduling lock table, in accordancewith some embodiments. A distributed scheduling lock table 350 may beconfigured to store values for a current index 360, a job count 365, anda scheduled end time 370. The current index 360 may have an initialvalue of zero. The job count 365 may have a value equal to a number ofjobs stored in the job table 345. The scheduled end time 370 may includea time value to indicate when a refresh is to occur. This may bedetermined based on a configurable refresh cycle 510 (shown in FIG. 5)and a startup time of the scheduling service. For example, if thestartup time of scheduling service is at 11:45 a.m., and the refreshcycle 510 is set at 15 minutes, then the scheduled end time 370 is 12:00p.m. The scheduled end time 370 may then be updated to 12:15 p.m. It maybe noted that if the refresh cycle 510 is shorter (e.g., 5 minutes),then the scheduling service may be refreshed more frequently.

For some embodiments, a job block 515 (shown in FIG. 5) may be set to avalue that corresponds to a maximum number of jobs to be allocated toeach of the machines in the cluster 302. The value of the job block 515may be configurable. Using the job block 515 may prevent each schedulerfrom being overloaded, and the jobs from the job table 345 aredistributed evenly across all the schedulers. For example, if the jobcount 365 has a value of 300,000, the job block has a value of 100,000,and the current index has a value of zero, then the first machine 305 inthe cluster 302 may be allocated jobs the first 100,000 jobs from job 0to job 99,999. For some embodiments, while the jobs are allocated to thefirst machine 305, the distributed scheduling lock table 350 may belocked. For some embodiments, the allocation of the jobs to a machinemay be performed by a scheduler associated with that machine. It may benoted the term allocation may include reading a block of jobs from thejob table 345 into a memory of a machine associated with a scheduler.The reading of the jobs may include reading the job definitionassociated with each job.

After the allocation of the jobs to the first machine 302, the currentindex 360 may be updated by adding the value of the current index 360 tothe value of the job block 515. In the current example, the currentindex 360 is updated to the value 100,000, and the distributedscheduling lock table 350 may be released or unlocked. This may enablethe second machine 306 in the cluster 302 to be allocated jobs from100,000 to 199,999. For some embodiments, optimistic locking may be usedto enable fast access to the distributed scheduling lock table 350. Anumeric version locking may be used as a basis for optimistic locking.The distributed scheduling lock table 350 may include a version field toenable repeated attempt to acquire the same version of the distributedscheduling lock table 350. For example, if the second machine 306 cannotacquire the distributed scheduling lock table 350 because it is stilllocked, the attempt to acquire may continue until successful or untilthe scheduling service is shut down. While the jobs are allocated to thesecond machine 306, the distributed scheduling lock table 350 may againbe locked. After the allocation of the jobs to the second machine 304,the current index 360 may be updated to the value 200,000, and thedistributed scheduling lock table 350 may be unlocked. This may enablethe third machine 307 in the cluster 302 to be allocated jobs from200,000 to 299,999. After that, the current index 360 may be updated tothe value 300,000, and the allocation of jobs may stop because thecurrent index 360 has a value that is the same as the value of the jobcount 365. At this time, all of the machines in the cluster 302 havereceived their shares of the jobs from the job table 345, and each isready to schedule their jobs. For some embodiments, the distributedscheduling lock table 350 may be stored in the same database as the jobtable 345 (shown in FIG. 3). For example, the distributed schedulinglock table 350 may be stored as a table with one row and three columns.

It may be noted that, although the examples described with FIG. 3 andFIG. 4 refer to having three machines, the number of machines andcorrespondingly the number of schedulers (or scheduler instances) mayvary depending on the values of the job count 365 and the job block 515.For example, if the job count 365 is 400,000 instead of 300,000, then afourth machine and scheduler may be created to service the jobs 300,000to 399,999 so that all of the jobs may be allocated and scheduled.

FIG. 5 shows an example of the schedulers using the distributedscheduling lock table to schedule jobs, in accordance with someembodiments. Diagram 500 includes machines 305, 306 and 307 in acluster, distributed scheduling lock table 350 and job table 345. Forsome embodiments, the block of jobs allocated to a machine may be readinto the memory of the machine prior to any scheduling operations. Thecurrent index 360 may be used as a pointer to an index of a job. Forexample, if the current index 360 has a value of 100,000, then it may beused as a pointer to point to a location of a job at index 100,000 inthe job table 345. Using the current index 360 and the job count 365, afirst block of jobs 511 may be read into the memory of the first machine305. A second block of jobs 516 may be read into the memory of thesecond machine 306. A third block of jobs 521 may be read into thememory of the third machine 307. Using the example of FIG. 4, the firstblock of jobs 511 may include jobs associated with index 0 to 99,999.Similarly, the second block of jobs 516 may include jobs associated withthe index 100,000 to 199,999, and the third block of jobs 521 mayinclude jobs associated with the index 200,000 to 299,999. Theallocation may continue to the next machine until all of the jobs in thejob table 345 are allocated.

The arrows pointing from the distributed scheduling lock table 350 tothe schedulers 310, 315 and 320 are meant to indicate that theinformation in the distributed scheduling lock table 350 is used bythose schedulers. The arrows from the job table 345 to the block ofallocated jobs 511, 516 and 521 are meant to indicate that the block ofjobs are read from the job table 345 into the memory of the associatedmachine.

For some embodiments, the reading of the jobs into the memory of amachine may be performed by the scheduler executing in that machine.Based on having access to the distributed scheduling lock table 350, ascheduler may access the current index 360 and compare a value of thecurrent index 360 with a value of the job count 365. If the schedulerdetermines that the value of the current index 360 is less than thevalue of the job count 365, then that may mean that there are more jobsfrom the job table 345 to be allocated. Those jobs may then be read bythe scheduler into the memory of the associated machine. For example,the first block of jobs 511 may be read by the scheduler 310 executingin the first machine 305. The scheduler 310 may then schedule the jobsfrom the memory of the first machine 305 instead of having to read thejobs from the storage device associated with the job table 345.Similarly, each of the schedulers 315 and 320 also schedules the jobsfrom the memory of the respective machine 306 and 307.

The scheduling of the jobs may end at the scheduled end time 370 whenthe schedulers on three machines 305, 306 and 307 may be disposed. Theprocess of allocating and scheduling of jobs may then be repeated andended at an updated scheduled end time 370. For example, if the currentscheduled end time is 12:00 pm and the refresh cycle is 15 minutes, thenthe updated scheduled end time may be at 12:15 pm.

The scheduled end time 370 may be determined based on a clock time of acomputing system that maintains the distributed scheduling lock table350. It may be possible that while the schedulers are scheduling thejobs for execution, the jobs in the job table 345 may be updated orrefreshed. The scheduled end time 370 may enable all the schedulers toget the updated jobs from the job store 345. The scheduled end time 370may also allow one machine to take over the load of another machine whenthere is a failover. For some embodiment, when the scheduling service isshut down, all of the scheduling operations may be terminated and thelock on the distributed scheduling lock table 350 may be released.

FIG. 6 shows a flowchart of an example process that may be performed bya scheduler to read jobs from a job table, in accordance with someembodiments. The process 600 may start at block 602. At block 605, ascheduler may successfully acquire the distributed scheduling lock table350. The distributed scheduling lock table 350 may then be locked. Atblock 610, the scheduler may retrieve a value of the job block 515. Forexample, the value of the job block 515 may be 100,000. At block 615,the scheduler may retrieve a value of the current index 360 from thedistributed scheduling lock table 350. For example, the value of thecurrent index 360 may be 200,000. At block 625, the scheduler may readinto a memory of its associated machine jobs from the job table 345. Thejobs may be determined based on the current index 360 and the job block515. The process 600 may then stop at block 630. As described above, theprocess 600 may be repeated with another scheduler until all the jobs inthe job table 345 are read into the memories of the appropriatemachines.

FIG. 7A shows a flowchart of an example of a process that may beperformed by a scheduler to determine whether there are jobs to bescheduled, in accordance with some embodiments. The process 700 maystart at block 702. At block 705, the scheduler may retrieve the currentindex 360 and the job count 365. At block 710, a comparison may beperformed to determine whether a value of the current index 360 is lessthan a value of the job count 365. If not, the process may stop at block725 because there are no more jobs in the job table 345 to be scheduled.From block 710, if the value of the current index 360 is less than thevalue of the job count 365, then the process may flow to block 715 wherejobs may be read from the job table 345 into a memory of a machineassociated with the scheduler. At block 720, the current index 360 maybe updated to reflect a next job block. The process may end at block 725for the current job block.

FIG. 7B shows a flow chart example of a process that may be performedbased on a refresh cycle, in accordance with some embodiments. Theprocess 740 may start at block 750. At block 755, a test may beperformed to determine if it is the scheduled end time. This may bedetermined based on a system clock of a machine and a value of thescheduled end time 370. If the system clock matches with the value ofthe scheduled end time, the scheduling service may be stopped. Theschedulers in a cluster may be disposed. At block 765, a test may beperformed to determine if the scheduled end time is related to ashutdown of the scheduling service. If it is, then the process may stopat block 785. From block 765, if it is not related to a shutdown, theprocess may flow to block 770 where a value of the scheduled end time370 may be updated based on a refresh cycle to generate a value for anext scheduled end time. At block 775, the current index may be reset.For example, the current index may be reset to zero. At block 780, thescheduling service may be restarted. Restarting the scheduling servicemay include performing the operations described with FIG. 6 and FIG. 7A.

FIG. 8A shows a system diagram 800 illustrating architectural componentsof an on-demand service environment, in accordance with someembodiments. A client machine located in the cloud 804 (or Internet) maycommunicate with the on-demand service environment via one or more edgerouters 808 and 812. The edge routers may communicate with one or morecore switches 820 and 824 via firewall 816. The core switches maycommunicate with a load balancer 828, which may distribute server loadover different pods, such as the pods 840 and 844. The pods 840 and 844,which may each include one or more servers and/or other computingresources, may perform data processing and other operations used toprovide on-demand services. Communication with the pods may be conductedvia pod switches 832 and 836. Components of the on-demand serviceenvironment may communicate with a database storage system 856 via adatabase firewall 848 and a database switch 852.

As shown in FIGS. 8A and 8B, accessing an on-demand service environmentmay involve communications transmitted among a variety of differenthardware and/or software components. Further, the on-demand serviceenvironment 800 is a simplified representation of an actual on-demandservice environment. For example, while only one or two devices of eachtype are shown in FIGS. 8A and 8B, some embodiments of an on-demandservice environment may include anywhere from one to many devices ofeach type. Also, the on-demand service environment need not include eachdevice shown in FIGS. 8A and 8B, or may include additional devices notshown in FIGS. 8A and 8B.

Moreover, one or more of the devices in the on-demand serviceenvironment 800 may be implemented on the same physical device or ondifferent hardware. Some devices may be implemented using hardware or acombination of hardware and software. Thus, terms such as “dataprocessing apparatus,” “machine,” “server” and “device” as used hereinare not limited to a single hardware device, but rather include anyhardware and software configured to provide the described functionality.

The cloud 804 is intended to refer to a data network or plurality ofdata networks, often including the Internet. Client machines located inthe cloud 804 may communicate with the on-demand service environment toaccess services provided by the on-demand service environment. Forexample, client machines may access the on-demand service environment toretrieve, store, edit, and/or process information.

In some embodiments, the edge routers 808 and 812 route packets betweenthe cloud 804 and other components of the on-demand service environment800. The edge routers 808 and 812 may employ the Border Gateway Protocol(BGP). The BGP is the core routing protocol of the Internet. The edgerouters 808 and 812 may maintain a table of IP networks or ‘prefixes’which designate network reachability among autonomous systems on theInternet.

In one or more embodiments, the firewall 816 may protect the innercomponents of the on-demand service environment 800 from Internettraffic. The firewall 816 may block, permit, or deny access to the innercomponents of the on-demand service environment 800 based upon a set ofrules and other criteria. The firewall 816 may act as one or more of apacket filter, an application gateway, a stateful filter, a proxyserver, or any other type of firewall.

In some embodiments, the core switches 820 and 824 are high-capacityswitches that transfer packets within the on-demand service environment800. The core switches 820 and 824 may be configured as network bridgesthat quickly route data between different components within theon-demand service environment. In some embodiments, the use of two ormore core switches 820 and 824 may provide redundancy and/or reducedlatency.

In some embodiments, the pods 840 and 844 may perform the core dataprocessing and service functions provided by the on-demand serviceenvironment. Each pod may include various types of hardware and/orsoftware computing resources. An example of the pod architecture isdiscussed in greater detail with reference to FIG. 8B.

In some embodiments, communication between the pods 840 and 844 may beconducted via the pod switches 832 and 836. The pod switches 832 and 836may facilitate communication between the pods 840 and 844 and clientmachines located in the cloud 804, for example via core switches 820 and824. Also, the pod switches 832 and 836 may facilitate communicationbetween the pods 840 and 844 and the database storage 856.

In some embodiments, the load balancer 828 may distribute workloadbetween the pods 840 and 844. Balancing the on-demand service requestsbetween the pods may assist in improving the use of resources,increasing throughput, reducing response times, and/or reducingoverhead. The load balancer 828 may include multilayer switches toanalyze and forward traffic.

In some embodiments, access to the database storage 856 may be guardedby a database firewall 848. The database firewall 848 may act as acomputer application firewall operating at the database applicationlayer of a protocol stack. The database firewall 848 may protect thedatabase storage 856 from application attacks such as structure querylanguage (SQL) injection, database rootkits, and unauthorizedinformation disclosure.

In some embodiments, the database firewall 848 may include a host usingone or more forms of reverse proxy services to proxy traffic beforepassing it to a gateway router. The database firewall 848 may inspectthe contents of database traffic and block certain content or databaserequests. The database firewall 848 may work on the SQL applicationlevel atop the TCP/IP stack, managing applications' connection to thedatabase or SQL management interfaces as well as intercepting andenforcing packets traveling to or from a database network or applicationinterface.

In some embodiments, communication with the database storage system 856may be conducted via the database switch 852. The multi-tenant databasesystem 856 may include more than one hardware and/or software componentsfor handling database queries. Accordingly, the database switch 852 maydirect database queries transmitted by other components of the on-demandservice environment (e.g., the pods 840 and 844) to the correctcomponents within the database storage system 856. In some embodiments,the database storage system 856 is an on-demand database system sharedby many different organizations.

The on-demand database system may employ a multi-tenant approach, avirtualized approach, or any other type of database approach. Anon-demand database system is discussed in greater detail with referenceto FIGS. 9 and 10.

FIG. 8B shows a system diagram illustrating the architecture of the pod844, in accordance with one embodiment. The pod 844 may be used torender services to a user of the on-demand service environment 800. Insome embodiments, each pod may include a variety of servers and/or othersystems. The pod 844 includes one or more content batch servers 864,content search servers 868, query servers 872, file force servers 876,access control system (ACS) servers 880, batch servers 884, and appservers 888. Also, the pod 844 includes database instances 890, quickfile systems (QFS) 892, and indexers 894. In one or more embodiments,some or all communication between the servers in the pod 844 may betransmitted via the switch 836.

In some embodiments, the application servers 888 may include a hardwareand/or software framework dedicated to the execution of procedures(e.g., programs, routines, scripts) for supporting the construction ofapplications provided by the on-demand service environment 800 via thepod 844. Some such procedures may include operations for providing theservices described herein. The content batch servers 864 may requestsinternal to the pod. These requests may be long-running and/or not tiedto a particular customer. For example, the content batch servers 864 mayhandle requests related to log mining, cleanup work, and maintenancetasks.

The content search servers 868 may provide query and indexer functions.For example, the functions provided by the content search servers 868may allow users to search through content stored in the on-demandservice environment. The Fileforce servers 876 may manage requestsinformation stored in the Fileforce storage 878. The Fileforce storage878 may store information such as documents, images, and basic largeobjects (BLOBs). By managing requests for information using theFileforce servers 876, the image footprint on the database may bereduced.

The query servers 872 may be used to retrieve information from one ormore file systems. For example, the query system 872 may receiverequests for information from the app servers 888 and then transmitinformation queries to the NFS 896 located outside the pod. The pod 844may share a database instance 890 configured as a multi-tenantenvironment in which different organizations share access to the samedatabase. Additionally, services rendered by the pod 844 may requirevarious hardware and/or software resources. In some embodiments, the ACSservers 880 may control access to data, hardware resources, or softwareresources.

In some embodiments, the batch servers 884 may process batch jobs, whichare used to run tasks at specified times. Thus, the batch servers 884may transmit instructions to other servers, such as the app servers 888,to trigger the batch jobs. For some embodiments, the QFS 892 may be anopen source file system available from Sun Microsystems® of Santa Clara,Calif. The QFS may serve as a rapid-access file system for storing andaccessing information available within the pod 844. The QFS 892 maysupport some volume management capabilities, allowing many disks to begrouped together into a file system. File system metadata can be kept ona separate set of disks, which may be useful for streaming applicationswhere long disk seeks cannot be tolerated. Thus, the QFS system maycommunicate with one or more content search servers 868 and/or indexers894 to identify, retrieve, move, and/or update data stored in thenetwork file systems 896 and/or other storage systems.

In some embodiments, one or more query servers 872 may communicate withthe NFS 896 to retrieve and/or update information stored outside of thepod 844. The NFS 896 may allow servers located in the pod 844 to accessinformation to access files over a network in a manner similar to howlocal storage is accessed. In some embodiments, queries from the queryservers 822 may be transmitted to the NFS 896 via the load balancer 820,which may distribute resource requests over various resources availablein the on-demand service environment. The NFS 896 may also communicatewith the QFS 892 to update the information stored on the NFS 896 and/orto provide information to the QFS 892 for use by servers located withinthe pod 844.

In some embodiments, the pod may include one or more database instances890. The database instance 890 may transmit information to the QFS 892.When information is transmitted to the QFS, it may be available for useby servers within the pod 844 without requiring an additional databasecall. In some embodiments, database information may be transmitted tothe indexer 894. Indexer 894 may provide an index of informationavailable in the database 890 and/or QFS 892. The index information maybe provided to file force servers 876 and/or the QFS 892.

FIG. 9 shows a block diagram of an environment 910 wherein an on-demanddatabase service might be used, in accordance with some embodiments.Environment 910 includes an on-demand database service 916. User system912 may be any machine or system that is used by a user to access adatabase user system. For example, any of user systems 912 can be ahandheld computing system, a mobile phone, a laptop computer, a workstation, and/or a network of computing systems. As illustrated in FIGS.9 and 10, user systems 912 might interact via a network 914 with theon-demand database service 916.

An on-demand database service, such as system 916, is a database systemthat is made available to outside users that do not need to necessarilybe concerned with building and/or maintaining the database system, butinstead may be available for their use when the users need the databasesystem (e.g., on the demand of the users). Some on-demand databaseservices may store information from one or more tenants stored intotables of a common database image to form a multi-tenant database system(MTS). Accordingly, “on-demand database service 916” and “system 916”will be used interchangeably herein. A database image may include one ormore database objects. A relational database management system (RDBMS)or the equivalent may execute storage and retrieval of informationagainst the database object(s). Application platform 918 may be aframework that allows the applications of system 916 to run, such as thehardware and/or software, e.g., the operating system. In animplementation, on-demand database service 916 may include anapplication platform 918 that enables creation, managing and executingone or more applications developed by the provider of the on-demanddatabase service, users accessing the on-demand database service viauser systems 912, or third party application developers accessing theon-demand database service via user systems 912.

One arrangement for elements of system 916 is shown in FIG. 9, includinga network interface 920, application platform 918, tenant data storage922 for tenant data 923, system data storage 924 for system data 925accessible to system 916 and possibly multiple tenants, program code 926for implementing various functions of system 916, and a process space928 for executing MTS system processes and tenant-specific processes,such as running applications as part of an application hosting service.Additional processes that may execute on system 916 include databaseindexing processes.

The users of user systems 912 may differ in their respective capacities,and the capacity of a particular user system 912 might be entirelydetermined by permissions (permission levels) for the current user. Forexample, where a call center agent is using a particular user system 912to interact with system 916, the user system 912 has the capacitiesallotted to that call center agent. However, while an administrator isusing that user system to interact with system 916, that user system hasthe capacities allotted to that administrator. In systems with ahierarchical role model, users at one permission level may have accessto applications, data, and database information accessible by a lowerpermission level user, but may not have access to certain applications,database information, and data accessible by a user at a higherpermission level. Thus, different users may have different capabilitieswith regard to accessing and modifying application and databaseinformation, depending on a user's security or permission level.

Network 914 is any network or combination of networks of devices thatcommunicate with one another. For example, network 914 can be any one orany combination of a LAN (local area network), WAN (wide area network),telephone network, wireless network, point-to-point network, starnetwork, token ring network, hub network, or other appropriateconfiguration. As the most common type of computer network in currentuse is a TCP/IP (Transfer Control Protocol and Internet Protocol)network (e.g., the Internet), that network will be used in many of theexamples herein. However, it should be understood that the networks usedin some embodiments are not so limited, although TCP/IP is a frequentlyimplemented protocol.

User systems 912 might communicate with system 916 using TCP/IP and, ata higher network level, use other common Internet protocols tocommunicate, such as HTTP, FTP, AFS, WAP, etc. In an example where HTTPis used, user system 912 might include an HTTP client commonly referredto as a “browser” for sending and receiving HTTP messages to and from anHTTP server at system 916. Such an HTTP server might be implemented asthe sole network interface between system 916 and network 914, but othertechniques might be used as well or instead. In some embodiments, theinterface between system 916 and network 914 includes load sharingfunctionality, such as round-robin HTTP request distributors to balanceloads and distribute incoming HTTP requests evenly over a plurality ofservers. At least as for the users that are accessing that server, eachof the plurality of servers has access to the MTS' data; however, otheralternative configurations may be used instead.

In some embodiments, system 916, shown in FIG. 9, implements a web-basedcustomer relationship management (CRM) system. For example, in someembodiments, system 916 includes application servers configured toimplement and execute CRM software applications as well as providerelated data, code, forms, web pages and other information to and fromuser systems 912 and to store to, and retrieve from, a database systemrelated data, objects, and Webpage content. With a multi-tenant system,data for multiple tenants may be stored in the same physical databaseobject, however, tenant data typically is arranged so that data of onetenant is kept logically separate from that of other tenants so that onetenant does not have access to another tenant's data, unless such datais expressly shared. In certain embodiments, system 916 implementsapplications other than, or in addition to, a CRM application. Forexample, system 916 may provide tenant access to multiple hosted(standard and custom) applications. User (or third party developer)applications, which may or may not include CRM, may be supported by theapplication platform 918, which manages creation, storage of theapplications into one or more database objects and executing of theapplications in a virtual machine in the process space of the system916.

Each user system 912 could include a desktop personal computer,workstation, laptop, PDA, cell phone, or any wireless access protocol(WAP) enabled device or any other computing system capable ofinterfacing directly or indirectly to the Internet or other networkconnection. User system 912 typically runs an HTTP client, e.g., abrowsing program, such as Microsoft's Internet Explorer® browser,Mozilla's Firefox® browser, Opera's browser, or a WAP-enabled browser inthe case of a cell phone, PDA or other wireless device, or the like,allowing a user (e.g., subscriber of the multi-tenant database system)of user system 912 to access, process and view information, pages andapplications available to it from system 916 over network 914.

Each user system 912 also typically includes one or more user interfacedevices, such as a keyboard, a mouse, trackball, touch pad, touchscreen, pen or the like, for interacting with a graphical user interface(GUI) provided by the browser on a display (e.g., a monitor screen, LCDdisplay, etc.) in conjunction with pages, forms, applications and otherinformation provided by system 916 or other systems or servers. Forexample, the user interface device can be used to access data andapplications hosted by system 916, and to perform searches on storeddata, and otherwise allow a user to interact with various GUI pages thatmay be presented to a user. As discussed above, embodiments are suitablefor use with the Internet, which refers to a specific globalinternetwork of networks. However, it should be understood that othernetworks can be used instead of the Internet, such as an intranet, anextranet, a virtual private network (VPN), a non-TCP/IP based network,any LAN or WAN or the like.

According to some embodiments, each user system 912 and all of itscomponents are operator configurable using applications, such as abrowser, including computer code run using a central processing unitsuch as an Intel Pentium® processor or the like. Similarly, system 916(and additional instances of an MTS, where more than one is present) andall of their components might be operator configurable usingapplication(s) including computer code to run using a central processingunit such as processor system 917, which may include an Intel Pentium®processor or the like, and/or multiple processor units.

A computer program product implementation includes a machine-readablestorage medium (media) having instructions stored thereon/in which canbe used to program a computer to perform any of the processes of theembodiments described herein. Computer code for operating andconfiguring system 916 to intercommunicate and to process web pages,applications and other data and media content as described herein arepreferably downloaded and stored on a hard disk, but the entire programcode, or portions thereof, may also be stored in any other volatile ornon-volatile memory medium or device, such as a ROM or RAM, or providedon any media capable of storing program code, such as any type ofrotating media including floppy disks, optical discs, digital versatiledisk (DVD), compact disk (CD), microdrive, and magneto-optical disks,and magnetic or optical cards, nanosystems (including molecular memoryICs), or any type of media or device suitable for storing instructionsand/or data. Additionally, the entire program code, or portions thereof,may be transmitted and downloaded from a software source over atransmission medium, e.g., over the Internet, or from another server, ortransmitted over any other conventional network connection (e.g.,extranet, VPN, LAN, etc.) using any communication medium and protocols(e.g., TCP/IP, HTTP, HTTPS, Ethernet, etc.). It will also be appreciatedthat computer code for implementing embodiments can be implemented inany programming language that can be executed on a client system and/orserver or server system such as, for example, C, C++, HTML, any othermarkup language, Java™, JavaScript®, ActiveX®, any other scriptinglanguage, such as VBScript, and many other programming languages as arewell known may be used. (Java™ is a trademark of Sun Microsystems®,Inc.).

According to some embodiments, each system 916 is configured to provideweb pages, forms, applications, data and media content to user (client)systems 912 to support the access by user systems 912 as tenants ofsystem 916. As such, system 916 provides security mechanisms to keepeach tenant's data separate unless the data is shared. If more than oneMTS is used, they may be located in close proximity to one another(e.g., in a server farm located in a single building or campus), or theymay be distributed at locations remote from one another (e.g., one ormore servers located in city A and one or more servers located in cityB). As used herein, each MTS could include logically and/or physicallyconnected servers distributed locally or across one or more geographiclocations. Additionally, the term “server” is meant to include acomputing system, including processing hardware and process space(s),and an associated storage system and database application (e.g., OODBMSor RDBMS) as is well known in the art.

It should also be understood that “server system” and “server” are oftenused interchangeably herein. Similarly, the database object describedherein can be implemented as single databases, a distributed database, acollection of distributed databases, a database with redundant online oroffline backups or other redundancies, etc., and might include adistributed database or storage network and associated processingintelligence.

FIG. 10 also shows a block diagram of environment 910 furtherillustrating system 916 and various interconnections, in accordance withsome embodiments. FIG. 10 shows that user system 912 may includeprocessor system 912A, memory system 912B, input system 912C, and outputsystem 912D. FIG. 10 shows network 914 and system 916. FIG. 10 alsoshows that system 916 may include tenant data storage 922, tenant data923, system data storage 924, system data 925, User Interface (UI) 1030,Application Program Interface (API) 1032, PL/SOQL 1034, save routines1036, application setup mechanism 1038, applications servers10001-1000N, system process space 1002, tenant process spaces 1004,tenant management process space 1010, tenant storage area 1012, userstorage 1014, and application metadata 1016. In other embodiments,environment 910 may not have the same elements as those listed aboveand/or may have other elements instead of, or in addition to, thoselisted above.

User system 912, network 914, system 916, tenant data storage 922, andsystem data storage 924 were discussed above in FIG. 9. Regarding usersystem 912, processor system 912A may be any combination of processors.Memory system 912B may be any combination of one or more memory devices,short term, and/or long term memory. Input system 912C may be anycombination of input devices, such as keyboards, mice, trackballs,scanners, cameras, and/or interfaces to networks. Output system 912D maybe any combination of output devices, such as monitors, printers, and/orinterfaces to networks. As shown by FIG. 10, system 916 may include anetwork interface 920 (of FIG. 9) implemented as a set of HTTPapplication servers 1000, an application platform 918, tenant datastorage 922, and system data storage 924. Also shown is system processspace 1002, including individual tenant process spaces 1004 and a tenantmanagement process space 1010. Each application server 1000 may beconfigured to tenant data storage 922 and the tenant data 923 therein,and system data storage 924 and the system data 925 therein to serverequests of user systems 912. The tenant data 923 might be divided intoindividual tenant storage areas 1012, which can be either a physicalarrangement and/or a logical arrangement of data. Within each tenantstorage area 1012, user storage 1014 and application metadata 1016 mightbe similarly allocated for each user. For example, a copy of a user'smost recently used (MRU) items might be stored to user storage 1014.Similarly, a copy of MRU items for an entire organization that is atenant might be stored to tenant storage area 1012. A UI 1030 provides auser interface and an API 1032 provides an application programmerinterface to system 916 resident processes to users and/or developers atuser systems 912. The tenant data and the system data may be stored invarious databases, such as Oracle™ databases.

Application platform 918 includes an application setup mechanism 1038that supports application developers' creation and management ofapplications, which may be saved as metadata into tenant data storage922 by save routines 1036 for execution by subscribers as tenant processspaces 1004 managed by tenant management process 1010 for example.Invocations to such applications may be coded using PL/SOQL 34 thatprovides a programming language style interface extension to API 1032. Adetailed description of some PL/SOQL language embodiments is discussedin commonly assigned U.S. Pat. No. 7,730,478, titled METHOD AND SYSTEMFOR ALLOWING ACCESS TO DEVELOPED APPLICATIONS VIA A MULTI-TENANTON-DEMAND DATABASE SERVICE, by Craig Weissman, filed Sep. 21, 4007,which is hereby incorporated by reference in its entirety and for allpurposes. Invocations to applications may be detected by systemprocesses, which manage retrieving application metadata 1016 for thesubscriber making the invocation and executing the metadata as anapplication in a virtual machine.

Each application server 1000 may be communicably coupled to databasesystems, e.g., having access to system data 925 and tenant data 923, viaa different network connection. For example, one application server10001 might be coupled via the network 914 (e.g., the Internet), anotherapplication server 1000N-1 might be coupled via a direct network link,and another application server 1000N might be coupled by yet a differentnetwork connection. Transfer Control Protocol and Internet Protocol(TCP/IP) are typical protocols for communicating between applicationservers 1000 and the database system. However, other transport protocolsmay be used to optimize the system depending on the network interconnectused.

In certain embodiments, each application server 1000 is configured tohandle requests for any user associated with any organization that is atenant. Because it is desirable to be able to add and remove applicationservers from the server pool at any time for any reason, there ispreferably no server affinity for a user and/or organization to aspecific application server 1000. In some embodiments, therefore, aninterface system implementing a load balancing function (e.g., an F5Big-IP load balancer) is communicably coupled between the applicationservers 1000 and the user systems 912 to distribute requests to theapplication servers 1000. In some embodiments, the load balancer uses aleast connections algorithm to route user requests to the applicationservers 1000. Other examples of load balancing algorithms, such as roundrobin and observed response time, also can be used. For example, incertain embodiments, three consecutive requests from the same user couldhit three different application servers 1000, and three requests fromdifferent users could hit the same application server 1000. In thismanner, system 916 is multi-tenant, wherein system 916 handles storageof, and access to, different objects, data and applications acrossdisparate users and organizations.

As an example of storage, one tenant might be a company that employs asales force where each call center agent uses system 916 to manage theirsales process. Thus, a user might maintain contact data, leads data,customer follow-up data, performance data, goals and progress data,etc., all applicable to that user's personal sales process (e.g., intenant data storage 922). In an example of a MTS arrangement, since allof the data and the applications to access, view, modify, report,transmit, calculate, etc., can be maintained and accessed by a usersystem having nothing more than network access, the user can manage hisor her sales efforts and cycles from any of many different user systems.For example, if a call center agent is visiting a customer and thecustomer has Internet access in their lobby, the call center agent canobtain critical updates as to that customer while waiting for thecustomer to arrive in the lobby.

While each user's data might be separate from other users' dataregardless of the employers of each user, some data might beorganization-wide data shared or accessible by a plurality of users orall of the users for a given organization that is a tenant. Thus, theremight be some data structures managed by system 916 that are allocatedat the tenant level while other data structures might be managed at theuser level. Because an MTS might support multiple tenants includingpossible competitors, the MTS should have security protocols that keepdata, applications, and application use separate. Also, because manytenants may opt for access to an MTS rather than maintain their ownsystem, redundancy, up-time, and backup are additional functions thatmay be implemented in the MTS. In addition to user-specific data andtenant specific data, system 916 might also maintain system level datausable by multiple tenants or other data. Such system level data mightinclude industry reports, news, postings, and the like that are sharableamong tenants.

In certain embodiments, user systems 912 (which may be clientmachines/systems) communicate with application servers 1000 to requestand update system-level and tenant-level data from system 916 that mayrequire sending one or more queries to tenant data storage 922 and/orsystem data storage 924. System 916 (e.g., an application server 1000 insystem 916) automatically generates one or more SQL statements (e.g.,SQL queries) that are designed to access the desired information. Systemdata storage 924 may generate query plans to access the requested datafrom the database.

Each database can generally be viewed as a collection of objects, suchas a set of logical tables, containing data fitted into predefinedcategories. A “table” is one representation of a data object, and may beused herein to simplify the conceptual description of objects and customobjects according to some embodiments. It should be understood that“table” and “object” may be used interchangeably herein. Each tablegenerally contains one or more data categories logically arranged ascolumns or fields in a viewable schema. Each row or record of a tablecontains an instance of data for each category defined by the fields.For example, a CRM database may include a table that describes acustomer with fields for basic contact information such as name,address, phone number, fax number, etc. Another table might describe apurchase order, including fields for information such as customer,product, sale price, date, etc. In some multi-tenant database systems,standard entity tables might be provided for use by all tenants. For CRMdatabase applications, such standard entities might include tables foraccount, contact, lead, and opportunity data, each containingpre-defined fields. It should be understood that the word “entity” mayalso be used interchangeably herein with “object” and “table”.

In some multi-tenant database systems, tenants may be allowed to createand store custom objects, or they may be allowed to customize standardentities or objects, for example by creating custom fields for standardobjects, including custom index fields. U.S. Pat. No. 7,779,039, titledCUSTOM ENTITIES AND FIELDS IN A MULTI-TENANT DATABASE SYSTEM, byWeissman, et al., and which is hereby incorporated by reference in itsentirety and for all purposes, teaches systems and methods for creatingcustom objects as well as customizing standard objects in a multi-tenantdatabase system. In some embodiments, for example, all custom entitydata rows are stored in a single multi-tenant physical table, which maycontain multiple logical tables per organization. In some embodiments,multiple “tables” for a single customer may actually be stored in onelarge table and/or in the same table as the data of other customers.

These and other aspects of the disclosure may be implemented by varioustypes of hardware, software, firmware, etc. For example, some featuresof the disclosure may be implemented, at least in part, bymachine-program product that include program instructions, stateinformation, etc., for performing various operations described herein.Examples of program instructions include both machine code, such asproduced by a compiler, and files containing higher-level code that maybe executed by the computer using an interpreter. Examples ofmachine-program product include, but are not limited to, magnetic mediasuch as hard disks, floppy disks, and magnetic tape; optical media suchas CD-ROM disks; magneto-optical media; and hardware devices that arespecially configured to store and perform program instructions, such asread-only memory devices (“ROM”) and random access memory (“RAM”).

While one or more embodiments and techniques are described withreference to an implementation in which a service cloud console isimplemented in a system having an application server providing a frontend for an on-demand database service capable of supporting multipletenants, the one or more embodiments and techniques are not limited tomulti-tenant databases nor deployment on application servers.Embodiments may be practiced using other database architectures, i.e.,ORACLE®, DB2® by IBM and the like without departing from the scope ofthe embodiments claimed.

Any of the above embodiments may be used alone or together with oneanother in any combination. Although various embodiments may have beenmotivated by various deficiencies with the prior art, which may bediscussed or alluded to in one or more places in the specification, theembodiments do not necessarily address any of these deficiencies. Inother words, different embodiments may address different deficienciesthat may be discussed in the specification. Some embodiments may onlypartially address some deficiencies or just one deficiency that may bediscussed in the specification, and some embodiments may not address anyof these deficiencies.

While various embodiments have been described herein, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of the present applicationshould not be limited by any of the embodiments described herein, butshould be defined only in accordance with the following andlater-submitted claims and their equivalents.

What is claimed is:
 1. A method comprising: storing by a first schedulerinto a memory of a first virtual machine running on a server computersystem, a first block of jobs to be executed by the first virtualmachine, the first block of jobs being included in a job table stored ina database and having a first block size, the database associated withthe server computer system; storing by a second scheduler into a memoryof a second virtual machine running on the server computer system, asecond block of jobs to be executed by the by the second virtualmachine, the second block of jobs being included in the job table andhaving a second block size, the second block size being equal to thefirst block size and including jobs that are not in included in thefirst block of jobs; scheduling by the first scheduler from the memoryof the first virtual machine, one or more jobs in the first block ofjobs for execution by the first virtual machine; and scheduling by thesecond scheduler from the memory of the second virtual machine, one ormore jobs in the second block of jobs for execution by the secondvirtual machine.
 2. The method of claim 1, wherein the first block ofjobs is determined based on an index pointing to a job in the job table,and the first block size used to determine jobs to be included in thefirst block of jobs.
 3. The method of claim 2, wherein the index pointsto a first job in the first block of jobs, and the index is updated topoint to a first job in the second block of jobs after the storing ofthe first block of jobs into the memory of the first virtual machine. 4.The method of claim 3, further comprising comparing the index to a totalnumber of jobs in the job table to determine whether there are jobsremaining in the job table to enable a third scheduler to store a thirdblock of jobs included in the job table into a memory of a third virtualmachine.
 5. The method of claim 4, further comprising at least accessingthe index and locking access to the index in order to compare the indexto the total number of jobs in the job table.
 6. The method of claim 5,wherein there are no remaining jobs in the job table for the thirdscheduler based on the index being equal to the total number of jobs inthe job table.
 7. The method of claim 6, wherein the scheduling of jobsby the first scheduler and the second scheduler is stopped based on anend of scheduling time.
 8. The method of claim 7, wherein the storing bythe first scheduler and the second scheduler is refreshed based on theend of scheduling time, the index is reset, and the end of schedulingtime is updated to a next end of scheduling time based on a configurablerefresh cycle.
 9. The method of claim 8, wherein the second scheduler isconfigured to schedule the jobs in the first block of jobs based on afailover of the first virtual machine.
 10. An apparatus comprising: oneor more processors; and a non-transitory computer readable mediumstoring a plurality of instructions, which when executed, cause the oneor more processors to: store by a first scheduler into a memory of afirst virtual machine running on a server computer system, a first blockof jobs to be executed by the first virtual machine, the first block ofjobs being included in a job table stored in a database and having afirst block size, the database associated with the server computersystem; store by a second scheduler into a memory of a second virtualmachine running on the server computer system, a second block of jobs tobe executed by the second virtual machine, the second block of jobsbeing included in the job table and having a second block size, thesecond block size being equal to the first block size and including jobsthat are not in included in the first block of jobs; schedule by thefirst scheduler from the memory of the first virtual machine, one ormore jobs in the first block of jobs for execution by the first virtualmachine; and schedule by the second scheduler from the memory of thesecond virtual machine, one or more jobs in the second block of jobs forexecution by the second virtual machine.
 11. The apparatus of claim 10,wherein the first block of jobs is determined based on an index pointingto a job in the job table and the first block size used to determinejobs to be included in the first block of jobs.
 12. The apparatus ofclaim 11, wherein the index points to a first job in the first block ofjobs, and the index is updated to point to a first job in the secondblock of jobs after the storing of the first block of jobs into thememory of the first virtual machine.
 13. The apparatus of claim 12,further comprising instructions to compare the index to a total numberof jobs in the job table to determine whether there are jobs remainingin the job table to enable a third scheduler to store a third block ofjobs included in the job table into a memory of a third virtual machine.14. The apparatus of claim 13, further comprising instructions to atleast access the index and to lock access to the index in order tocompare the index to the total number of jobs in the job table.
 15. Theapparatus of claim 14, wherein there are no remaining jobs in the jobtable for the third scheduler based on the index being equal to thetotal number of jobs in the job table.
 16. The apparatus of claim 15,wherein the instructions to schedule jobs by the first scheduler and thesecond scheduler include instructions to stop scheduling based on an endof scheduling time.
 17. The apparatus of claim 16, wherein the storingby the first scheduler and the second scheduler is refreshed based onthe end of scheduling time, the index is reset, and the end ofscheduling time is updated to a next end of scheduling time based on aconfigurable refresh cycle.
 18. The apparatus of claim 17, wherein thesecond scheduler is configured to schedule the jobs in the first blockof jobs based on a failover of the first virtual machine.
 19. A computerprogram product comprising computer-readable program code to be executedby one or more processors when retrieved from a non-transitorycomputer-readable medium, the program code including instructions to:store by a first scheduler into a memory of a first virtual machinerunning on a server computer system, a first block of jobs to beexecuted by the first virtual machine, the first block of jobs beingincluded in a job table stored in a database and having a first blocksize, the database associated with the server computer system; store bya second scheduler into a memory of a second virtual machine running onthe server computer system, a second block of jobs to be executed by thesecond virtual machine, the second block of jobs being included in thejob table and having a second block size, the second block size beingequal to the first block size and including jobs that are not inincluded in the first block of jobs; schedule by the first schedulerfrom the memory of the first virtual machine, one or more jobs in thefirst block of jobs for execution by the first virtual machine; andschedule by the second scheduler from the memory of the second virtualmachine, one or more jobs in the second block of jobs for execution bythe second virtual machine.
 20. The computer program product of claim19, wherein the first block of jobs is determined based on an indexpointing to a job in the job table.
 21. The computer program product ofclaim 20, wherein the index points to a first job in the first block ofjobs, and the index is updated to point to a first job in the secondblock of jobs after the storing of the first block of jobs into thememory of the first virtual machine.
 22. The computer program product ofclaim 21, further comprising instructions to compare the index to atotal number of jobs in the job table to determine whether there arejobs remaining in the job table to enable a third scheduler to store athird block of jobs included in the job table into a memory of a thirdvirtual machine.
 23. The computer program product of claim 22, furthercomprising instructions to at least access the index and to lock accessto the index in order to compare the index to the total number of jobsin the job table.
 24. The computer program product of claim 23, whereinthere are no remaining jobs in the job table for the third schedulerbased on the index being equal to the total number of jobs in the jobtable.
 25. The computer program product of claim 24, wherein theinstructions to schedule jobs by the first scheduler and the secondscheduler include instructions to stop scheduling based on an end ofscheduling time.
 26. The computer program product of claim 25, whereinthe storing by the first scheduler and the second scheduler is refreshedbased on the end of scheduling time, the index is reset, and the end ofscheduling time is updated to a next end of scheduling time based on aconfigurable refresh cycle.
 27. The computer program product of claim26, wherein the second scheduler is configured to schedule the jobs inthe first block of jobs based on a failover of the first virtualmachine.